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Filters

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This page has been automatically translated using the Google Translate API services. We are working on improving texts. Thank you for your understanding and patience.

In addition to procedural image generation, direct pixel manipulation has another great utility: Image filters. To apply them, first, we will get a buffer with the original value of the pixels by image_pixels. A filter is nothing more than a function that changes the color of each point to achieve the desired effect. In this example we implement the convolution algorithm which needs to know the neighborhood environment of each point to process the effect (Figure 1). Depending on the values assigned to the convolution matrix, we will obtain different results. The source code is in folder /src/demo/filters of the SDK distribution.

  • Use image_from_pixels to create a new image with the modified pixels.
  • Capture an application with image filters. Windows version.
    Figure 1: Filters application, Windows version.
    Capture an application with image filters. macOS version.
    Figure 2: macOS version.
    Capture an application with image filters. Linux version.
    Figure 3: Linux version.
Listing 1: demo/filters/filters.c
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/* NAppGUI Hello World */

#include "nappgui.h"
#include "all.h"

typedef struct _app_t App;

struct _app_t
{
    Window *window;
    Image *image;
    ImageView *view;
    Cell *slider;
    uint32_t filter;
    real32_t angle;
};

/*---------------------------------------------------------------------------*/

static const uint32_t i_IDENT_SIZE = 3;
static const real32_t i_IDENT_FACTOR = 1;
static const real32_t i_IDENT_BIAS = 0;
static const real32_t i_IDENT_FILTER[] =
{
    0, 0, 0,
    0, 1, 0,
    0, 0, 0
};


static const uint32_t i_BLUR_SIZE = 5;
static const real32_t i_BLUR_FACTOR = 1.f / 256.f;
static const real32_t i_BLUR_BIAS = 0;
static const real32_t i_BLUR_FILTER[] =
{
    1,  4,  6,  4,  1,
    4, 16, 24, 16,  4,
    6, 24, 36, 24,  6,
    4, 16, 24, 16,  4,
    1,  4,  6,  4,  1,
};

static const uint32_t i_MOTION_SIZE = 9;
static const real32_t i_MOTION_FACTOR = 1.f / 9.f;
static const real32_t i_MOTION_BIAS = 0;
static const real32_t i_MOTION_FILTER[] =
{
  1, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 1, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 1, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 1, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 1, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 1, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 1, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 1, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 1,
};

static const uint32_t i_EDGE_SIZE = 5;
static const real32_t i_EDGE_FACTOR = 1;
static const real32_t i_EDGE_BIAS = 0;
static const real32_t i_EDGE_FILTER[] =
{
    -1,  0,  0,  0,  0,
    0, -2,  0,  0,  0,
    0,  0,  6,  0,  0,
    0,  0,  0, -2,  0,
    0,  0,  0,  0, -1,
};

static const uint32_t i_SHARPEN_SIZE = 3;
static const real32_t i_SHARPEN_FACTOR = 1;
static const real32_t i_SHARPEN_BIAS = 0;
static const real32_t i_SHARPEN_FILTER[] =
{
    1, 1, 1,
    1, -7, 1,
    1, 1, 1
};

static const uint32_t i_EMBOSS_SIZE = 3;
static const real32_t i_EMBOSS_FACTOR = 1;
static const real32_t i_EMBOSS_BIAS = 128;
static const real32_t i_EMBOSS_FILTER[] =
{
    -1, -1,  0,
    -1,  0,  1,
    0,  1,  1
};

/*---------------------------------------------------------------------------*/

static void i_apply_filter(App *app)
{
    Pixbuf *pixbuf = NULL;
    Pixbuf *output = NULL;
    Image *image = NULL;

    image_pixels(app->image, ekFIMAGE, &pixbuf, NULL);

    switch (app->filter) {
    case 0:
        output = pixbuf_convolution(pixbuf, i_IDENT_FILTER, i_IDENT_SIZE, i_IDENT_SIZE, i_IDENT_FACTOR, i_IDENT_BIAS);
        break;
    case 1:
        output = pixbuf_convolution(pixbuf, i_BLUR_FILTER, i_BLUR_SIZE, i_BLUR_SIZE, i_BLUR_FACTOR, i_BLUR_BIAS);
        break;
    case 2:
        output = pixbuf_convolution(pixbuf, i_MOTION_FILTER, i_MOTION_SIZE, i_MOTION_SIZE, i_MOTION_FACTOR, i_MOTION_BIAS);
        break;
    case 3:
        output = pixbuf_convolution(pixbuf, i_EDGE_FILTER, i_EDGE_SIZE, i_EDGE_SIZE, i_EDGE_FACTOR, i_EDGE_BIAS);
        break;
    case 4:
        output = pixbuf_convolution(pixbuf, i_SHARPEN_FILTER, i_SHARPEN_SIZE, i_SHARPEN_SIZE, i_SHARPEN_FACTOR, i_SHARPEN_BIAS);
        break;
    case 5:
        output = pixbuf_convolution(pixbuf, i_EMBOSS_FILTER, i_EMBOSS_SIZE, i_EMBOSS_SIZE, i_EMBOSS_FACTOR, i_EMBOSS_BIAS);
        break;
    case 6:
        output = pixbuf_rotate(pixbuf, (real32_t)(pixbuf_width(pixbuf) / 2), (real32_t)(pixbuf_height(pixbuf) / 2), app->angle * kBMATH_PIf, TRUE, ekINTERP_NONE, color_gray(240));
        break;
    cassert_default();
    }

    cell_enabled(app->slider, app->filter == 6);
    image = image_from_pixbuf(output, NULL);
    imageview_image(app->view, image);
    pixbuf_destroy(&pixbuf);
    pixbuf_destroy(&output);
    image_destroy(&image);
}

/*---------------------------------------------------------------------------*/

static void i_OnButton(App *app, Event *e)
{
    const EvButton *p = event_params(e, EvButton);
    app->filter = p->index;
    i_apply_filter(app);
}

/*---------------------------------------------------------------------------*/

static void i_OnSlider(App *app, Event *e)
{
    const EvSlider *p = event_params(e, EvSlider);
    app->angle = p->pos;
    i_apply_filter(app);
}

/*---------------------------------------------------------------------------*/

static Panel *i_panel(App *app)
{
    Panel *panel = panel_create();
    Layout *layout1 = layout_create(1, 2);
    Layout *layout2 = layout_create(8, 1);
    Layout *layout3 = layout_create(2, 1);
    Button *button1 = button_radio();
    Button *button2 = button_radio();
    Button *button3 = button_radio();
    Button *button4 = button_radio();
    Button *button5 = button_radio();
    Button *button6 = button_radio();
    Button *button7 = button_radio();
    Slider *slider = slider_create();
    ImageView *view1 = imageview_create();
    ImageView *view2 = imageview_create();
    uint32_t w, h;
    button_text(button1, "Identity");
    button_text(button2, "Blur");
    button_text(button3, "Motion");
    button_text(button4, "Edge");
    button_text(button5, "Sharpen");
    button_text(button6, "Emboss");
    button_text(button7, "Rotation");
    button_state(button3, ekON);
    button_OnClick(button1, listener(app, i_OnButton, App));
    slider_OnMoved(slider, listener(app, i_OnSlider, App));
    image_size(app->image, &w, &h);
    imageview_image(view1, app->image);
    imageview_image(view2, app->image);
    imageview_size(view1, s2di(w, h));
    imageview_size(view2, s2di(w, h));
    layout_button(layout2, button1, 0, 0);
    layout_button(layout2, button2, 1, 0);
    layout_button(layout2, button3, 2, 0);
    layout_button(layout2, button4, 3, 0);
    layout_button(layout2, button5, 4, 0);
    layout_button(layout2, button6, 5, 0);
    layout_button(layout2, button7, 6, 0);
    layout_slider(layout2, slider, 7, 0);
    layout_imageview(layout3, view1, 0, 0);
    layout_imageview(layout3, view2, 1, 0);
    layout_layout(layout1, layout2, 0, 0);
    layout_layout(layout1, layout3, 0, 1);
    layout_margin(layout1, 10);
    layout_hmargin(layout2, 0, 15);
    layout_hmargin(layout2, 1, 15);
    layout_hmargin(layout2, 2, 15);
    layout_hmargin(layout2, 3, 15);
    layout_hmargin(layout2, 4, 15);
    layout_hmargin(layout2, 5, 15);
    layout_vmargin(layout1, 0, 5);
    layout_hmargin(layout3, 0, 5);
    layout_hexpand(layout2, 7);
    panel_layout(panel, layout1);
    app->slider = layout_cell(layout2, 7, 0);
    app->view = view2;
    return panel;
}

/*---------------------------------------------------------------------------*/

static void i_OnClose(App *app, Event *e)
{
    osapp_finish();
    unref(app);
    unref(e);
}

/*---------------------------------------------------------------------------*/

static App *i_create(void)
{
    App *app = heap_new0(App);
    ResPack *pack = all_respack("");
    Panel *panel = NULL;
    app->image = image_copy(image_from_resource(pack, IMAGE_JPG));
    panel = i_panel(app);
    app->window = window_create(ekWNSTD, &panel);
    app->filter = 2;
    i_apply_filter(app);
    window_title(app->window, "Image Filters");
    window_origin(app->window, v2df(500, 200));
    window_OnClose(app->window, listener(app, i_OnClose, App));
    window_show(app->window);
    respack_destroy(&pack);
    return app;
}

/*---------------------------------------------------------------------------*/

static void i_destroy(App **app)
{
    window_destroy(&(*app)->window);
    image_destroy(&(*app)->image);
    heap_delete(app, App);
}

/*---------------------------------------------------------------------------*/

#include "osmain.h"
osmain(i_create, i_destroy, "", App)
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